If it works correctly you should see a square moving from the upper left to the lower right, with a little yellow box at the top of the moving square.
You can pass --target as a command line option to have it use a render target instead of rendering directly to the screen. The output should be identical in this case.
If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.
Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.
